Abstract: We determine the energy it takes to move a test quark along a circle ofradius L with angular frequency w through the strongly coupled plasma of N=4supersymmetric Yang-Mills SYM theory. We find that for most values of L and wthe energy deposited by stirring the plasma in this way is governed either bythe drag force acting on a test quark moving through the plasma in a straightline with speed v=Lw or by the energy radiated by a quark in circular motion inthe absence of any plasma, whichever is larger. There is a continuous crossoverfrom the drag-dominated regime to the radiation-dominated regime. In thecrossover regime we find evidence for significant destructive interferencebetween energy loss due to drag and that due to radiation as if in vacuum. Therotating quark thus serves as a model system in which the relative strength of,and interplay between, two different mechanisms of parton energy loss isaccessible via a controlled classical gravity calculation. We close byspeculating on the implications of our results for a quark that is movingthrough the plasma in a straight line while decelerating, although in this casethe classical calculation breaks down at the same value of the deceleration atwhich the radiation-dominated regime sets in.